US20110139506A1 - Pressure and flow control in drilling operations - Google Patents

Abstract

A well drilling system for use with a drilling fluid pump includes a flow control device regulating flow from the pump to a drill string interior; and another flow control device regulating flow through a line in communication with an annulus. Flow is simultaneously permitted through the flow control devices. A method of maintaining a desired bottom hole pressure includes dividing drilling fluid flow between a line in communication with a drill string interior and a line in communication with an annulus; the flow dividing step including permitting flow through a flow control device interconnected between a pump and the drill string interior; and the flow dividing step including permitting flow through another flow control device interconnected between the pump and the annulus, while flow is permitted through the first flow control device.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• The present application claims the benefit under 35 USC §119 of the filing date of International Application No. PCT/US08/87686, filed Dec. 19, 2008. The entire disclosure of this prior application is incorporated herein by this reference.
BACKGROUND
• The present disclosure relates generally to equipment utilized and operations performed in conjunction with well drilling operations and, in an embodiment described herein, more particularly provides for pressure and flow control in drilling operations.
• Managed pressure drilling is well known as the art of precisely controlling bottom hole pressure during drilling by utilizing a closed annulus and a means for regulating pressure in the annulus. The annulus is typically closed during drilling through use of a rotating control device (RCD, also known as a rotating control head or rotating blowout preventer) which seals about the drill pipe as it rotates.
• The means for regulating pressure in the annulus can include a choke interconnected in the mud return line and, in some applications, a backpressure pump to apply pressure to the annulus while connections are made in the drill pipe string. Unfortunately, use of a backpressure pump requires substantial capital investment, the additional pump takes up scarce space on offshore rigs, the pump output is difficult to control accurately and use of the pump interferes with normal operations on a drilling rig.
• Therefore, it may be seen that improvements are needed in the art of controlling pressure and flow in drilling operations. These improvements may include the elimination of a separate backpressure pump in drilling operations, but the improvements could be utilized in conjunction with a backpressure pump, if desired.
SUMMARY
• In carrying out the principles of the present disclosure, systems and methods are provided which solve at least one problem in the art. One example is described below in which flow through a standpipe line and flow through a bypass line are independently variable, thereby enabling more accurate control over flow and pressure during the drilling operation. Another example is described below in which, after a drill pipe connection is made, the standpipe line and drill pipe are filled and pressurized prior to closing off flow through the bypass line.
• In one aspect, a well drilling system is provided by the disclosure below for use with a pump which pumps drilling fluid through a drill string while drilling a wellbore. The system includes a flow control device which regulates flow from the pump to an interior of the drill string, and another flow control device which regulates flow from the pump through a line in communication with an annulus formed between the drill string and the wellbore. Flow is simultaneously permitted through the flow control devices.
• In another aspect, a method of maintaining a desired bottom hole pressure during a well drilling operation is provided. The method includes the step of: dividing flow of drilling fluid between a line in communication with an interior of a drill string and a line in communication with an annulus formed between the drill string and a wellbore. The flow dividing step includes permitting flow through a flow control device interconnected between a pump and the interior of the drill string. The flow dividing step further includes permitting flow through another flow control device interconnected between the pump and the annulus, while flow is permitted through the first flow control device.
• In yet another aspect, a method of making a connection in a drill string, while maintaining a desired bottom hole pressure, includes the steps of:
• pumping a drilling fluid from a rig mud pump and through a mud return choke during the entire connection making method;
• determining a desired annulus pressure which corresponds to the desired bottom hole pressure during the entire connection making method, the annulus being formed between the drill string and a wellbore;
• regulating flow of the drilling fluid through the mud return choke, thereby maintaining the desired annulus pressure, during the entire connection making method;
• increasing flow through a bypass flow control device and decreasing flow through a standpipe flow control device, thereby diverting at least a portion of the drilling fluid flow from a line in communication with an interior of the drill string to a line in communication with the annulus;
• preventing flow through the standpipe flow control device;
• then making the connection in the drill string; and
• then decreasing flow through the bypass flow control device and increasing flow through the standpipe flow control device, thereby diverting at least a portion of the drilling fluid flow to the line in communication with the interior of the drill string from the line in communication with the annulus.
• These and other features, advantages, benefits and objects will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the disclosure hereinbelow and the accompanying drawings, in which similar elements are indicated in the various figures using the same reference numbers.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a schematic view of a well drilling system and method embodying principles of the present disclosure;
• FIG. 2 is a schematic view of another configuration of the well drilling system;
• FIG. 3 is a schematic view of a pressure and flow control system which may be used in the well drilling system and method; and
• FIG. 4 is a flowchart of a method for making a drill string connection which may be used in the well drilling system and method.
DETAILED DESCRIPTION
• It is to be understood that the various embodiments of the present disclosure described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of the present disclosure. The embodiments are described merely as examples of useful applications of the principles of the disclosure, which is not limited to any specific details of these embodiments.
• In the following description of the representative embodiments of the disclosure, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used for convenience in referring to the accompanying drawings. In general, “above”, “upper”, “upward” and similar terms refer to a direction toward the earth's surface along a wellbore, and “below”, “lower”, “downward” and similar terms refer to a direction away from the earth's surface along the wellbore.
• Representatively and schematically illustrated inFIG. 1 is a welldrilling system10 and associated method which embody principles of the present disclosure. In thesystem10, awellbore12 is drilled by rotating adrill bit14 on an end of adrill string16. Drillingfluid18, commonly known as mud, is circulated downward through thedrill string16, out thedrill bit14 and upward through anannulus20 formed between the drill string and thewellbore12, in order to cool the drill bit, lubricate the drill string, remove cuttings and provide a measure of bottom hole pressure control. A non-return valve21 (typically a flapper-type check valve) prevents flow of thedrilling fluid18 upward through the drill string16 (e.g., when connections are being made in the drill string).
• Control of bottom hole pressure is very important in managed pressure drilling, and in other types of drilling operations. Preferably, the bottom hole pressure is accurately controlled to prevent excessive loss of fluid into the earth formation surrounding thewellbore12, undesired fracturing of the formation, undesired influx of formation fluids into the wellbore, etc. In typical managed pressure drilling, it is desired to maintain the bottom hole pressure just greater than a pore pressure of the formation, without exceeding a fracture pressure of the formation. In typical underbalanced drilling, it is desired to maintain the bottom hole pressure somewhat less than the pore pressure, thereby obtaining a controlled influx of fluid from the formation.
• Nitrogen or another gas, or another lighter weight fluid, may be added to thedrilling fluid18 for pressure control. This technique is useful, for example, in underbalanced drilling operations.
• In thesystem10, additional control over the bottom hole pressure is obtained by closing off the annulus20 (e.g., isolating it from communication with the atmosphere and enabling the annulus to be pressurized at or near the surface) using a rotating control device22 (RCD). The RCD22 seals about thedrill string16 above awellhead24. Although not shown inFIG. 1, thedrill string16 would extend upwardly through theRCD22 for connection to, for example, a rotary table (not shown), astandpipe line26, kelley (not shown), a top drive and/or other conventional drilling equipment.
• Thedrilling fluid18 exits thewellhead24 via awing valve28 in communication with theannulus20 below the RCD22. Thefluid18 then flows throughmud return lines30,73 to achoke manifold32, which includes redundant chokes34 (only one of which may be used at a time). Backpressure is applied to theannulus20 by variably restricting flow of thefluid18 through the operative choke(s)34.
• The greater the restriction to flow through thechoke34, the greater the backpressure applied to theannulus20. Thus, bottom hole pressure can be conveniently regulated by varying the backpressure applied to theannulus20. A hydraulics model can be used, as described more fully below, to determine a pressure applied to theannulus20 at or near the surface which will result in a desired bottom hole pressure, so that an operator (or an automated control system) can readily determine how to regulate the pressure applied to the annulus at or near the surface (which can be conveniently measured) in order to obtain the desired bottom hole pressure.
• Pressure applied to theannulus20 can be measured at or near the surface via a variety ofpressure sensors36,38,40, each of which is in communication with the annulus.Pressure sensor36 senses pressure below theRCD22, but above a blowout preventer (BOP)stack42.Pressure sensor38 senses pressure in the wellhead below theBOP stack42.Pressure sensor40 senses pressure in themud return lines30,73 upstream of thechoke manifold32.
• Anotherpressure sensor44 senses pressure in thestandpipe line26. Yet anotherpressure sensor46 senses pressure downstream of thechoke manifold32, but upstream of aseparator48,shaker50 andmud pit52. Additional sensors includetemperature sensors54,56,Coriolis flowmeter58, andflowmeters62,64,66.
• Not all of these sensors are necessary. For example, thesystem10 could include only two of the threeflowmeters62,64,66. However, input from the sensors is useful to the hydraulics model in determining what the pressure applied to theannulus20 should be during the drilling operation.
• In addition, thedrill string16 may include itsown sensors60, for example, to directly measure bottom hole pressure.Such sensors60 may be of the type known to those skilled in the art as pressure while drilling (PWD), measurement while drilling (MWD) and/or logging while drilling (LWD). These drill string sensor systems generally provide at least pressure measurement, and may also provide temperature measurement, detection of drill string characteristics (such as vibration, weight on bit, stick-slip, etc.), formation characteristics (such as resistivity, density, etc.) and/or other measurements. Various forms of telemetry (acoustic, pressure pulse, electromagnetic, etc.) may be used to transmit the downhole sensor measurements to the surface.
• Additional sensors could be included in thesystem10, if desired. For example, anotherflowmeter67 could be used to measure the rate of flow of the fluid18 exiting thewellhead24, another Coriolis flowmeter (not shown) could be interconnected directly upstream or downstream of arig mud pump68, etc.
• Fewer sensors could be included in thesystem10, if desired. For example, the output of therig mud pump68 could be determined by counting pump strokes, instead of by usingflowmeter62 or any other flowmeters.
• Note that theseparator48 could be a 3 or 4 phase separator, or a mud gas separator (sometimes referred to as a “poor boy degasser”). However, theseparator48 is not necessarily used in thesystem10.
• Thedrilling fluid18 is pumped through thestandpipe line26 and into the interior of thedrill string16 by therig mud pump68. Thepump68 receives the fluid18 from themud pit52 and flows it via astandpipe manifold70 to thestandpipe26, the fluid then circulates downward through thedrill string16, upward through theannulus20, through themud return lines30,73, through thechoke manifold32, and then via theseparator48 andshaker50 to themud pit52 for conditioning and recirculation.
• Note that, in thesystem10 as so far described above, thechoke34 cannot be used to control backpressure applied to theannulus20 for control of the bottom hole pressure, unless the fluid18 is flowing through the choke.
• In conventional overbalanced drilling operations, such a situation will arise whenever a connection is made in the drill string16 (e.g., to add another length of drill pipe to the drill string as thewellbore12 is drilled deeper), and the lack of circulation will require that bottom hole pressure be regulated solely by the density of the fluid18.
• In thesystem10, however, flow of the fluid18 through thechoke34 can be maintained, even though the fluid does not circulate through thedrill string16 andannulus20, while a connection is being made in the drill string. Thus, pressure can still be applied to theannulus20 by restricting flow of the fluid18 through thechoke34, even though a separate backpressure pump may not be used.
• Instead, the fluid18 is flowed from thepump68 to thechoke manifold32 via abypass line72,75 when a connection is made in thedrill string16. Thus, the fluid18 can bypass thestandpipe line26,drill string16 andannulus20, and can flow directly from thepump68 to themud return line30, which remains in communication with theannulus20. Restriction of this flow by thechoke34 will thereby cause pressure to be applied to theannulus20.
• As depicted inFIG. 1, both of thebypass line75 and themud return line30 are in communication with theannulus20 via asingle line73. However, thebypass line75 and themud return line30 could instead be separately connected to thewellhead24, for example, using an additional wing valve (e.g., below the RCD22), in which case each of thelines30,75 would be directly in communication with theannulus20. Although this might require some additional plumbing at the rig site, the effect on the annulus pressure would be essentially the same as connecting thebypass line75 and themud return line30 to thecommon line73. Thus, it should be appreciated that various different configurations of the components of thesystem10 may be used, without departing from the principles of this disclosure.
• Flow of the fluid18 through thebypass line72,75 is regulated by a choke or other type offlow control device74.Line72 is upstream of the bypassflow control device74, andline75 is downstream of the bypass flow control device.
• Flow of the fluid18 through thestandpipe line26 is substantially controlled by a valve or other type offlow control device76. Note that theflow control devices74,76 are independently controllable, which provides substantial benefits to thesystem10, as described more fully below.
• Since the rate of flow of the fluid18 through each of the standpipe andbypass lines26,72 is useful in determining how bottom hole pressure is affected by these flows, theflowmeters64,66 are depicted inFIG. 1 as being interconnected in these lines. However, the rate of flow through thestandpipe line26 could be determined even if only theflowmeters62,64 were used, and the rate of flow through thebypass line72 could be determined even if only theflowmeters62,66 were used. Thus, it should be understood that it is not necessary for thesystem10 to include all of the sensors depicted inFIG. 1 and described herein, and the system could instead include additional sensors, different combinations and/or types of sensors, etc.
• In another beneficial feature of thesystem10, a bypassflow control device78 and flowrestrictor80 may be used for filling thestandpipe line26 anddrill string16 after a connection is made, and equalizing pressure between the standpipe line andmud return lines30,73 prior to opening theflow control device76. Otherwise, sudden opening of theflow control device76 prior to thestandpipe line26 anddrill string16 being filled and pressurized with the fluid18 could cause an undesirable pressure transient in the annulus20 (e.g., due to flow to thechoke manifold32 temporarily being lost while the standpipe line and drill string fill with fluid, etc.).
• By opening the standpipe bypassflow control device78 after a connection is made, the fluid18 is permitted to fill thestandpipe line26 anddrill string16 while a substantial majority of the fluid continues to flow through thebypass line72, thereby enabling continued controlled application of pressure to theannulus20. After the pressure in thestandpipe line26 has equalized with the pressure in themud return lines30,73 andbypass line75, theflow control device76 can be opened, and then theflow control device74 can be closed to slowly divert a greater proportion of the fluid18 from thebypass line72 to thestandpipe line26.
• Before a connection is made in thedrill string16, a similar process can be performed, except in reverse, to gradually divert flow of the fluid18 from thestandpipe line26 to thebypass line72 in preparation for adding more drill pipe to thedrill string16. That is, theflow control device74 can be gradually opened to slowly divert a greater proportion of the fluid18 from thestandpipe line26 to thebypass line72, and then theflow control device76 can be closed.
• Note that theflow control device78 and flowrestrictor80 could be integrated into a single element (e.g., a flow control device having a flow restriction therein), and theflow control devices76,78 could be integrated into a single flow control device81 (e.g., a single choke which can gradually open to slowly fill and pressurize thestandpipe line26 anddrill string16 after a drill pipe connection is made, and then open fully to allow maximum flow while drilling).
• However, since typical conventional drilling rigs are equipped with theflow control device76 in the form of a valve in thestandpipe manifold70, and use of the standpipe valve is incorporated into usual drilling practices, the individually operableflow control devices76,78 are presently preferred. Theflow control devices76,78 are at times referred to collectively below as though they are the singleflow control device81, but it should be understood that theflow control device81 can include the individualflow control devices76,78.
• Another alternative is representatively illustrated inFIG. 2. In this configuration of thesystem10, theflow control device78 is in the form of a choke, and theflow restrictor80 is not used. Theflow control device78 depicted inFIG. 2 enables more precise control over the flow of the fluid18 into thestandpipe line26 anddrill string16 after a drill pipe connection is made.
• Note that each of theflow control devices74,76,78 and chokes34 are preferably remotely and automatically controllable to maintain a desired bottom hole pressure by maintaining a desired annulus pressure at or near the surface. However, any one or more of theseflow control devices74,76,78 and chokes34 could be manually controlled without departing from the principles of this disclosure.
• A pressure and flowcontrol system90 which may be used in conjunction with thesystem10 and associated methods ofFIGS. 1 & 2 is representatively illustrated inFIG. 3. Thecontrol system90 is preferably fully automated, although some human intervention may be used, for example, to safeguard against improper operation, initiate certain routines, update parameters, etc.
• Thecontrol system90 includes ahydraulics model92, a data acquisition andcontrol interface94 and a controller96 (such as a programmable logic controller or PLC, a suitably programmed computer, etc.). Although theseelements92,94,96 are depicted separately inFIG. 3, any or all of them could be combined into a single element, or the functions of the elements could be separated into additional elements, other additional elements and/or functions could be provided, etc.
• Thehydraulics model92 is used in thecontrol system90 to determine the desired annulus pressure at or near the surface to achieve the desired bottom hole pressure. Data such as well geometry, fluid properties and offset well information (such as geothermal gradient and pore pressure gradient, etc.) are utilized by thehydraulics model92 in making this determination, as well as real-time sensor data acquired by the data acquisition andcontrol interface94.
• Thus, there is a continual two-way transfer of data and information between thehydraulics model92 and the data acquisition andcontrol interface94. For the purposes of this disclosure, it is important to appreciate that the data acquisition andcontrol interface94 operates to maintain a substantially continuous flow of real-time data from thesensors44,54,66,62,64,60,58,46,36,38,40,56,67 to thehydraulics model92, so that the hydraulics model has the information it needs to adapt to changing circumstances and to update the desired annulus pressure, and the hydraulics model operates to supply the data acquisition and control interface substantially continuously with a value for the desired annulus pressure.
• A suitable hydraulics model for use as thehydraulics model92 in thecontrol system90 is REAL TIME HYDRAULICS™ provided by Halliburton Energy Services, Inc. of Houston, Tex. USA. Another suitable hydraulics model is provided under the trade name IRIS™, and yet another is available from SINTEF of Trondheim, Norway. Any suitable hydraulics model may be used in thecontrol system90 in keeping with the principles of this disclosure.
• A suitable data acquisition and control interface for use as the data acquisition andcontrol interface94 in thecontrol system90 are SENTRY™ and INSITE™ provided by Halliburton Energy Services, Inc. Any suitable data acquisition and control interface may be used in thecontrol system90 in keeping with the principles of this disclosure.
• Thecontroller96 operates to maintain a desired setpoint annulus pressure by controlling operation of themud return choke34. When an updated desired annulus pressure is transmitted from the data acquisition andcontrol interface94 to thecontroller96, the controller uses the desired annulus pressure as a setpoint and controls operation of thechoke34 in a manner (e.g., increasing or decreasing flow through the choke as needed) to maintain the setpoint pressure in theannulus20.
• This is accomplished by comparing the setpoint pressure to a measured annulus pressure (such as the pressure sensed by any of thesensors36,38,40), and increasing flow through thechoke34 if the measured pressure is greater than the setpoint pressure, and decreasing flow through the choke if the measured pressure is less than the setpoint pressure. Of course, if the setpoint and measured pressures are the same, then no adjustment of thechoke34 is required. This process is preferably automated, so that no human intervention is required, although human intervention may be used if desired.
• Thecontroller96 may also be used to control operation of the standpipeflow control devices76,78 and the bypassflow control device74. Thecontroller96 can, thus, be used to automate the processes of diverting flow of the fluid18 from thestandpipe line26 to thebypass line72 prior to making a connection in thedrill string16, then diverting flow from the bypass line to the standpipe line after the connection is made, and then resuming normal circulation of the fluid18 for drilling. Again, no human intervention may be required in these automated processes, other than to initiate each process in turn.
• Referring additionally now toFIG. 4, a schematic flowchart is provided for amethod100 for making a drill pipe connection in thewell drilling system10 using thecontrol system90. Of course, themethod100 may be used in other well drilling systems, and with other control systems, in keeping with the principles of this disclosure.
• The drill pipe connection process begins atstep102, in which the process is initiated. A drill pipe connection is typically made when thewellbore12 has been drilled far enough that thedrill string16 must be elongated in order to drill further.
• Instep104, the flow rate output of thepump68 may be decreased. By decreasing the flow rate of the fluid18 output from thepump68, it is more convenient to maintain thechoke34 within its most effective operating range (typically, from about 30% to about 70% of maximum opening) during the connection process. However, this step is not necessary if, for example, thechoke34 would otherwise remain within its effective operating range.
• Instep106, the setpoint pressure changes due to the reduced flow of the fluid18 (e.g., to compensate for decreased fluid friction in theannulus20 between thebit14 and thewing valve28 resulting in reduced equivalent circulating density). The data acquisition andcontrol interface94 receives indications (e.g., from thesensors58,60,62,66,67) that the flow rate of the fluid18 has decreased, and thehydraulics model92 in response determines that a changed annulus pressure is desired to maintain the desired bottom hole pressure, and thecontroller96 uses the changed desired annulus pressure as a setpoint to control operation of thechoke34.
• In a slightly overbalanced managed pressure drilling operation, the setpoint pressure would likely increase, due to the reduced equivalent circulating density, in which case flow through thechoke34 would be decreased in response. However, in some operations (such as, underbalanced drilling operations in which gas or another light weight fluid is added to thedrilling fluid18 to decrease bottom hole pressure), the setpoint pressure could decrease (e.g., due to production of liquid downhole).
• Instep108, the restriction to flow of the fluid18 through thechoke34 is changed, due to the changed desired annulus pressure instep106. As discussed above, thecontroller96 controls operation of thechoke34, in this case changing the restriction to flow through the choke to obtain the changed setpoint pressure. Also as discussed above, the setpoint pressure could increase or decrease.
• Steps104,106 and108 are depicted in theFIG. 4 flowchart as being performed concurrently, since the setpoint pressure and mud return choke restriction can continuously vary, whether in response to each other, in response to the change in the mud pump output and in response to other conditions, as discussed above.
• Instep109, the bypassflow control device74 gradually opens. This diverts a gradually increasing proportion of the fluid18 to flow through thebypass line72, instead of through thestandpipe line26.
• Instep110, the setpoint pressure changes due to the reduced flow of the fluid18 through the drill string16 (e.g., to compensate for decreased fluid friction in theannulus20 between thebit14 and thewing valve28 resulting in reduced equivalent circulating density). Flow through thedrill string16 eventually ceases when the bypassflow control device74 is opened, since thebypass line72 becomes the path of least resistance to flow. The data acquisition andcontrol interface94 receives indications (e.g., from thesensors58,60,62,66,67) that the flow rate of the fluid18 through thedrill pipe16 andannulus20 has decreased, and thehydraulics model92 in response determines that a changed annulus pressure is desired to maintain the desired bottom hole pressure, and thecontroller96 uses the changed desired annulus pressure as a setpoint to control operation of thechoke34.
• In a slightly overbalanced managed pressure drilling operation, the setpoint pressure would likely increase, due to the reduced equivalent circulating density, in which case flow through thechoke34 would be decreased in response. However, in some operations (such as, underbalanced drilling operations in which gas or another light weight fluid is added to thedrilling fluid18 to decrease bottom hole pressure), the setpoint pressure could decrease (e.g., due to production of liquid downhole).
• Instep111, the restriction to flow of the fluid18 through thechoke34 is changed, due to the changed desired annulus pressure instep110. As discussed above, thecontroller96 controls operation of thechoke34, in this case changing the restriction to flow through the choke to obtain the changed setpoint pressure. Also as discussed above, the setpoint pressure could increase or decrease.
• Steps109,110 and111 are depicted in theFIG. 4 flowchart as being performed concurrently, since the setpoint pressure and mud return choke restriction can continuously vary, whether in response to each other, in response to the bypassflow control device74 opening and in response to other conditions, as discussed above.
• Instep112, the pressures in thestandpipe line26 and theannulus20 at or near the surface (indicated bysensors36,38,40,44) equalize. At this point, the bypassflow control device74 should be fully open, and substantially all of the fluid18 is flowing through thebypass line72,75 and not through the standpipe line26 (since the bypass line represents the path of least resistance). Static pressure in thestandpipe line26 should substantially equalize with pressure in thelines30,73,75 upstream of thechoke manifold32.
• Instep114, the standpipeflow control device81 is closed. The separate standpipe bypassflow control device78 should already be closed, in which case only thevalve76 would be closed instep114.
• Instep116, a standpipe bleed valve (not shown) would be opened to bleed pressure and fluid from thestandpipe line26 in preparation for breaking the connection between the kelley or top drive and thedrill string16. At this point, thestandpipe line26 is vented to atmosphere.
• Instep118, the kelley or top drive is broken off of thedrill string16, another stand of drill pipe is connected to the drill string, and the kelley or top drive is made up to the top of the drill string. This step is performed in accordance with conventional drilling practice.
• Instep120, the standpipe bleed valve is closed. Thestandpipe line26 is, thus, isolated again from atmosphere, but the standpipe line and the newly added stand of drill pipe is substantially empty (i.e., not filled with the fluid18) and un-pressurized.
• Instep122, the standpipe bypassflow control device78 opens (in the case of the valve and flow restrictor configuration ofFIG. 1) or gradually opens (in the case of the choke configuration ofFIG. 2). In this manner, the fluid18 is allowed to fill thestandpipe line26 and the newly added stand of drill pipe, as indicated instep124.
• Eventually, the pressure in thestandpipe line26 will equalize with the pressure in theannulus20 at or near the surface, as indicated instep126. However, substantially all of the fluid18 will still flow through thebypass line72 at this point. Static pressure in thestandpipe line26 should substantially equalize with pressure in thelines30,73,75 upstream of thechoke manifold32.
• Instep128, the standpipeflow control device76 is opened in preparation for diverting flow of the fluid18 to thestandpipe line26 and thence through thedrill string16. The standpipe bypassflow control device78 is then closed. Note that, by previously filling thestandpipe line26 anddrill string16, and equalizing pressures between the standpipe line and theannulus20, the step of opening the standpipeflow control device76 does not cause any significant undesirable pressure transients in the annulus ormud return lines30,73. Substantially all of the fluid18 still flows through thebypass line72, instead of through thestandpipe line26, even though the standpipeflow control device76 is opened.
• Considering the separate standpipeflow control devices76,78 as a single standpipeflow control device81, then the flow control device is gradually opened to slowly fill thestandpipe line26 anddrill string16, and then fully opened when pressures in the standpipe line andannulus20 are substantially equalized.
• Instep130, the bypassflow control device74 is gradually closed, thereby diverting an increasingly greater proportion of the fluid18 to flow through thestandpipe line26 anddrill string16, instead of through thebypass line72. During this step, circulation of the fluid18 begins through thedrill string16 andwellbore12.
• Instep132, the setpoint pressure changes due to the flow of the fluid18 through thedrill string16 and annulus20 (e.g., to compensate for increased fluid friction resulting in increased equivalent circulating density). The data acquisition andcontrol interface94 receives indications (e.g., from thesensors60,64,66,67) that the flow rate of the fluid18 through thewellbore12 has increased, and thehydraulics model92 in response determines that a changed annulus pressure is desired to maintain the desired bottom hole pressure, and thecontroller96 uses the changed desired annulus pressure as a setpoint to control operation of thechoke34. The desired annulus pressure may either increase or decrease, as discussed above forsteps106 and108.
• Instep134, the restriction to flow of the fluid18 through thechoke34 is changed, due to the changed desired annulus pressure instep132. As discussed above, thecontroller96 controls operation of thechoke34, in this case changing the restriction to flow through the choke to obtain the changed setpoint pressure.
• Steps130,132 and134 are depicted in theFIG. 4 flowchart as being performed concurrently, since the setpoint pressure and mud return choke restriction can continuously vary, whether in response to each other, in response to the bypassflow control device74 closing and in response to other conditions, as discussed above.
• Instep135, the flow rate output from thepump68 may be increased in preparation for resuming drilling of thewellbore12. This increased flow rate maintains thechoke34 in its optimum operating range, but this step (as withstep104 discussed above) may not be used if the choke is otherwise maintained in its optimum operating range.
• Instep136, the setpoint pressure changes due to the increased flow of the fluid18 (e.g., to compensate for increased fluid friction in theannulus20 between thebit14 and thewing valve28 resulting in increased equivalent circulating density). The data acquisition andcontrol interface94 receives indications (e.g., from thesensors58,60,62,66,67) that the flow rate of the fluid18 has increased, and thehydraulics model92 in response determines that a changed annulus pressure is desired to maintain the desired bottom hole pressure, and thecontroller96 uses the changed desired annulus pressure as a setpoint to control operation of thechoke34.
• In a slightly overbalanced managed pressure drilling operation, the setpoint pressure would likely decrease, due to the increased equivalent circulating density, in which case flow through thechoke34 would be increased in response.
• Instep137, the restriction to flow of the fluid18 through thechoke34 is changed, due to the changed desired annulus pressure instep136. As discussed above, thecontroller96 controls operation of thechoke34, in this case changing the restriction to flow through the choke to obtain the changed setpoint pressure. Also as discussed above, the setpoint pressure could increase or decrease.
• Steps135,136 and137 are depicted in theFIG. 4 flowchart as being performed concurrently, since the setpoint pressure and mud return choke restriction can continuously vary, whether in response to each other, in response to the change in the mud pump output and in response to other conditions, as discussed above.
• Instep138, drilling of thewellbore12 resumes. When another connection is needed in thedrill string16, the steps102-138 can be repeated.
• Steps140 and142 are included in theFIG. 4 flowchart for theconnection method100 to emphasize that thecontrol system90 continues to operate throughout the method. That is, the data acquisition andcontrol interface94 continues to receive data from thesensors36,38,40,44,46,54,56,58,62,64,66,67 and supplies appropriate data to thehydraulics model92. Thehydraulics model92 continues to determine the desired annulus pressure corresponding to the desired bottom hole pressure. Thecontroller96 continues to use the desired annulus pressure as a setpoint pressure for controlling operation of thechoke34.
• It will be appreciated that all or most of the steps described above may be conveniently automated using thecontrol system90. For example, thecontroller96 may be used to control operation of any or all of theflow control devices34,74,76,78,81 automatically in response to input from the data acquisition andcontrol interface94.
• Human intervention would preferably be used to indicate to thecontrol system90 when it is desired to begin the connection process (step102), and then to indicate when a drill pipe connection has been made (step118), but substantially all of the other steps could be automated (i.e., by suitably programming the software elements of the control system90). However, it is envisioned that all of the steps102-142 can be automated, for example, if a suitable top drive drilling rig (or any other drilling rig which enables drill pipe connections to be made without human intervention) is used.
• It may now be fully appreciated that the above disclosure provides substantial improvements to the art of pressure and flow control in drilling operations. Among these improvements is elimination of the necessity for use of a separate backpressure pump to maintain annulus pressure during drill pipe connections. Also among these improvements is the coordinated gradual diversion ofdrilling fluid18 between thestandpipe line26 andbypass line72 in a manner which eliminates, or at least substantially eliminates, undesirable pressure transients in theannulus20 when connections are made.
• The above disclosure provides awell drilling system10 for use with apump68 which pumpsdrilling fluid18 through adrill string16 while drilling awellbore12. Aflow control device81 regulates flow from thepump68 to an interior of thedrill string16. Anotherflow control device74 regulates flow from thepump68 to aline75 in communication with anannulus20 formed between thedrill string16 and thewellbore12. Flow is simultaneously permitted through theflow control devices74,81.
• Theflow control device81 may be operable independently from operation of theflow control device74.
• Thepump68 may be a rig mud pump in communication via theflow control device81 with astandpipe line26 for supplying thedrilling fluid18 to the interior of thedrill string16. Thesystem10 is preferably free of any other pump which applies pressure to theannulus20.
• Thesystem10 can also include anotherflow control device34 which variably restricts flow from theannulus20. Anautomated control system90 may control operation of theflow control devices34,74 to maintain a desired annulus pressure while a connection is made in thedrill string16. Thecontrol system90 may also control operation of theflow control device81 to maintain the desired annulus pressure while the connection is made in thedrill string16.
• The above disclosure also describes a method of maintaining a desired bottom hole pressure during a well drilling operation. The method includes the steps of: dividing flow ofdrilling fluid18 between aline26 in communication with an interior of adrill string16 and aline75 in communication with anannulus20 formed between thedrill string16 and awellbore12; the flow dividing step including permitting flow through a standpipeflow control device81 interconnected between apump68 and the interior of thedrill string16; and the flow dividing step including permitting flow through a bypassflow control device74 interconnected between thepump68 and theannulus20, while flow is permitted through the standpipeflow control device81.
• The method may also include the step of closing the standpipeflow control device81 after pressures in theline26 in communication with the interior of thedrill string16 and theline75 in communication with theannulus20 equalize.
• The method may include the steps of: making a connection in thedrill string16 after the step of closing the standpipeflow control device81; then permitting flow through the standpipeflow control device81 while permitting flow through the bypassflow control device74; and then closing the bypassflow control device74 after pressures again equalize in theline26 in communication with the interior of thedrill string16 and in theline75 in communication with theannulus20.
• The method may also include the step of permitting flow through another flow control device (e.g., choke34) continuously during the flow dividing, standpipe flow control device closing, connection making and bypass flow control device closing steps, thereby maintaining a desired annulus pressure corresponding to the desired bottom hole pressure.
• The method may also include the step of determining the desired annulus pressure in response to input of sensor measurements to ahydraulics model92 during the drilling operation. The step of maintaining the desired annulus pressure may include automatically varying flow through the flow control device (e.g., choke34) in response to comparing a measured annulus pressure with the desired annulus pressure.
• The above disclosure also describes amethod100 of making a connection in adrill string16 while maintaining a desired bottom hole pressure. Themethod100 includes the steps of:
• pumping adrilling fluid18 from arig mud pump68 and through a mud return choke34 during the entireconnection making method100;
• determining a desired annulus pressure which corresponds to the desired bottom hole pressure during the entireconnection making method100, theannulus20 being formed between thedrill string16 and awellbore12;
• regulating flow of thedrilling fluid18 through themud return choke34, thereby maintaining the desired annulus pressure, during the entireconnection making method100;
• increasing flow through a bypassflow control device74 and decreasing flow through a standpipeflow control device81, thereby diverting at least a portion of the drilling fluid flow from aline26 in communication with an interior of thedrill string16 to aline75 in communication with theannulus20;
• preventing flow through the standpipeflow control device81;
• then making the connection in thedrill string16; and
• then decreasing flow through the bypassflow control device74 and increasing flow through the standpipeflow control device81, thereby diverting at least another portion of the drilling fluid flow to theline26 in communication with the interior of thedrill string16 from theline75 in communication with theannulus20.
• The steps of increasing flow through the bypassflow control device74 and decreasing flow through the standpipeflow control device81 may also include simultaneously permitting flow through the bypass and standpipeflow control devices74,81.
• The steps of decreasing flow through the bypassflow control device74 and increasing flow through the standpipeflow control device81 further comprise simultaneously permitting flow through the bypass and standpipeflow control devices74,81.
• Themethod100 may also include the step of equalizing pressure between theline26 in communication with the interior of thedrill string16 and theline75 in communication with theannulus20. This pressure equalizing step is preferably performed after the step of increasing flow through the bypassflow control device74, and prior to the step of decreasing flow through the standpipeflow control device81.
• Themethod100 may also include the step of equalizing pressure between theline26 in communication with the interior of thedrill string16 and theline75 in communication with theannulus20. This pressure equalizing step is preferably performed after the step of decreasing flow through the bypassflow control device74, and prior to the step of increasing flow through the standpipeflow control device81.
• The step of determining the desired annulus pressure may include determining the desired annulus pressure in response to input of sensor measurements to ahydraulics model92. The step of maintaining the desired annulus pressure may include automatically varying flow through the mud return choke34 in response to comparing a measured annulus pressure with the desired annulus pressure.
• Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the disclosure, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to the specific embodiments, and such changes are contemplated by the principles of the present disclosure. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims and their equivalents.

Claims (19)

1. A well drilling system for use with a pump which pumps drilling fluid through a drill string while drilling a wellbore, the system comprising:

a first flow control device which regulates flow from the pump to an interior of the drill string;

a second flow control device which regulates flow from the pump through a line in communication with an annulus formed between the drill string and the wellbore; and

wherein flow is simultaneously permitted through the first and second flow control devices.

2. The system ofclaim 1, wherein the first flow control device is operable independently from operation of the second flow control device.

3. The system ofclaim 1, wherein the pump is a rig mud pump in communication via the first flow control device with a standpipe line for supplying the drilling fluid to the interior of the drill string.

4. The system ofclaim 1, wherein the pump is a rig mud pump, and wherein the system is free of any other pump which applies pressure to the annulus.

5. The system ofclaim 1, further comprising a third flow control device which variably restricts flow from the annulus, and wherein an automated control system controls operation of the second and third flow control devices to maintain a desired annulus pressure while a connection is made in the drill string.

6. The system ofclaim 5, wherein the control system further controls operation of the first flow control device to maintain the desired annulus pressure while the connection is made in the drill string.

7. A method of maintaining a desired bottom hole pressure during a well drilling operation, the method comprising the steps of:

dividing flow of drilling fluid between a line in communication with an interior of a drill string and a line in communication with an annulus formed between the drill string and a wellbore;

the flow dividing step including permitting flow through a first flow control device interconnected between a pump and the interior of the drill string; and

the flow dividing step including permitting flow through a second flow control device interconnected between the pump and the annulus, while flow is permitted through the first flow control device.

8. The method ofclaim 7, further comprising the step of closing the first flow control device after pressures in the line in communication with the interior of the drill string and the line in communication with the annulus equalize.

9. The method ofclaim 8, further comprising the steps of:

making a connection in the drill string after the first flow control device closing step;

then permitting flow through the first flow control device while permitting flow through the second flow control device; and

then closing the second flow control device after pressures again equalize in the line in communication with the interior of the drill string and in the line in communication with the annulus.

10. The method ofclaim 9, further comprising the step of permitting flow through a third flow control device continuously during the flow dividing, first flow control device closing, connection making and second flow control device closing steps, thereby maintaining a desired annulus pressure corresponding to the desired bottom hole pressure.

11. The method ofclaim 10, further comprising the step of determining the desired annulus pressure in response to input of sensor measurements to a hydraulics model during the drilling operation.

12. The method ofclaim 11, wherein the step of maintaining the desired annulus pressure further comprises automatically varying flow through the third flow control device in response to comparing a measured annulus pressure with the desired annulus pressure.

13. A method of making a connection in a drill string while maintaining a desired bottom hole pressure, the method comprising the steps of:

pumping a drilling fluid from a rig mud pump and through a mud return choke during the entire connection making method;

determining a desired annulus pressure which corresponds to the desired bottom hole pressure during the entire connection making method;

regulating flow of the drilling fluid through the mud return choke, thereby maintaining the desired annulus pressure, during the entire connection making method;

increasing flow through a bypass flow control device and decreasing flow through a standpipe flow control device, thereby diverting at least a first portion of the drilling fluid flow from a line in communication with an interior of the drill string to a line in communication with an annulus;

preventing flow through the standpipe flow control device;

then making the connection in the drill string; and

then decreasing flow through the bypass flow control device and increasing flow through the standpipe flow control device, thereby diverting at least a second portion of the drilling fluid flow to the line in communication with the interior of the drill string from the line in communication with the annulus.

14. The method ofclaim 13, wherein the steps of increasing flow through the bypass flow control device and decreasing flow through the standpipe flow control device further comprise simultaneously permitting flow through the bypass and standpipe flow control devices.

15. The method ofclaim 13, wherein the steps of decreasing flow through the bypass flow control device and increasing flow through the standpipe flow control device further comprise simultaneously permitting flow through the bypass and standpipe flow control devices.

16. The method ofclaim 13, further comprising the step of equalizing pressure between the line in communication with the interior of the drill string and the line in communication with the annulus, the pressure equalizing step being performed after the step of increasing flow through the bypass flow control device, and the pressure equalizing step being performed prior to the step of decreasing flow through the standpipe flow control device.

17. The method ofclaim 13, further comprising the step of equalizing pressure between the line in communication with the interior of the drill string and the line in communication with the annulus, the pressure equalizing step being performed after the step of decreasing flow through the bypass flow control device, and the pressure equalizing step being performed prior to the step of increasing flow through the standpipe flow control device.

18. The method ofclaim 13, wherein the step of determining the desired annulus pressure further comprises determining the desired annulus pressure in response to input of sensor measurements to a hydraulics model.

19. The method ofclaim 18, wherein the step of maintaining the desired annulus pressure further comprises automatically varying flow through the mud return choke in response to comparing a measured annulus pressure with the desired annulus pressure.

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